The invention relates to electrometallurgy, and more specifically to apparatus for the electroslag remelting of consumable electrodes.
Although electroslag remelting has been practised for a comparatively long time, there is as yet no adequate solution of some problems connected with a service life of moulds and with a decrease in impurities in the metal of an ingot.
There exists a variety of apparatus for practising the electroslag remelting of metals, on the whole similar in design and comprising a bottom plate, a mould, and an a.c. power source connected to electrode holders, as is disclosed in British Pat. No. 1,168,900 and Belgian Pat. No. 707,566. The electrode holders carry consumable electrodes which are introduced into the mould, whereupon electric current is passed through them, and slag is melted down therewith in the mould. Thereafter, as the consumable electrodes fuse, under the liquid slag layer a metal pool is formed, which progressively crystallizes to form an ingot. The disadvantage of apparatus of this type consists in a deficient removal of gases from the metal pool due to both anodic electrochemical reaction and cathodic electrochemical reaction, none of which prevails over the other, and whch takes place on the liquid slag--liquid metal interface.
This disadvantage is largely overcome in an apparatus for the electroslag remelting of consumable electrodes disclosed in U.S. Pat. No. 3,652,733 which makes it possible to control chemical reactions in the molten slag on the metal pool - slag pool interface, which promotes more efficient refinement of the molten metal from inclusions of sulphur, oxygen and hydrogen. The above apparatus comprises a bottom plate and a mould which are electrically connected to each other and to one terminal of an a.c. power source, an electrode holder adapted to hold at least one consumable electrode being connected to another terminal of said a.c. power source, and an electrode holder adapted to hold at least one nonconsumable electrode being connected through rectifiers to different terminals of the a.c. source. Said rectifiers provide for superimposition of direct current onto alternating current passing through the slag pool. This being the case, the metal pool during the major part of the time is a cathode, which promotes more efficient refinement of the molten metal from sulphur, oxygen and hydrogen.
However, alongside evident advantages, the foregoing apparatus has a substantial disadvantage. Specifically, as alternating current flows through the mould, the mould wall suffers from spark discharge during the half-cycle when it is an anode. During the same half-cycle, sulphur and oxygen anions and hydroxyl anions discharge on the slag - metal pool interface, which is accompanied by the reverse transition of sulphur, oxygen and hydrogen from the slag into the ingot metal, which reduces the efficiency of refining the ingot metal.